http://d.puremagic.com/issues/show_bug.cgi?id=879

           Summary: support for --gc-sections
           Product: D
           Version: 1.00
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: thomas-dloop@kuehne.cn


--gc-sections is ld's flag to "Enable garbage collection of unused input sections."

As known(#100 and #101) it currently breaks DMD's exception handling on Linux. I think I've found the cause and know a simple fix.

#
# void main(){
#    throw new Exception("message");
# }
#

dmd a.d -ofa; nm --numeric-sort a
[...]
> 000000000805c4b0 R _D3std6thread6Thread6__vtblZ
> 000000000805c508 R _deh_beg
> 000000000805c508 r _TMP3
> 000000000805c514 r _TMP1
[...]
> 000000000805c604 r _TMP14
> 000000000805c610 r _TMP27
> 000000000805c61c R _deh_end
> 000000000805c61c r __FRAME_END__
[...]

dmd a.d -ofa -L--gc-sections; nm --numeric-sort a
> [...]
> 0000000008053270 R _D3std6thread6Thread6__vtblZ
> 00000000080532c8 R _deh_beg
> 00000000080532c8 R _deh_end
> 00000000080532c8 r __FRAME_END__
> [...]

The missing _TMP... symbols are of type internal.deh2.FuncTable and describe where to find the exception handlers of a given function.

BUG 1:
ld rightfully removed those as they are never directly referenced. However they
are accessed indirectly via _deh_beg and _deh_end (-> internal/deh2.d:98-100).

FIX 1:
Define an elf symbol with the following characteristics:
address:  _deh_beg
size: _deh_end - _deh_beg + sizeof(_deh_end)
and ensure that this symbol is guaranteed to be referenced somewhere regardless
of compiler flags like -O, -release and -inline.

BUG 2:
from above:
> 00000000080532c8 R _deh_beg
> 00000000080532c8 R _deh_end
> 00000000080532c8 r __FRAME_END__
_deh_beg, _deh_end and __FRAME_END__ have the same addresses because _deh_beg and _deh_end claim to be of size zero.

FIX 2:
The same as #472, please emit correct size information for all elf symbols.


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #1 from thomas-dloop@kuehne.cn  2007-03-31 15:08 -------
Created an attachment (id=106)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=106&action=view)
Binutils workaround


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #2 from thomas-dloop@kuehne.cn  2007-04-04 15:39 -------
Daniel Jacobowitz suggested a much more straight forward solution on the binutils mailing list(http://sourceware.org/ml/binutils/):

> Another way to fix this would be to emit R_arch_NONE relocations from the code sections to the EH tables they require.


-- 

d-bugmail@puremagic.com wrote:
> ------- Comment #2 from thomas-dloop@kuehne.cn  2007-04-04 15:39 -------
> Daniel Jacobowitz suggested a much more straight forward solution on the binutils mailing list(http://sourceware.org/ml/binutils/):
> 
>> Another way to fix this would be to emit R_arch_NONE relocations from
>> the code sections to the EH tables they require.

Interesting. And should be easy enough to implement.
An added advantage to this approach would be that no relatively new version of binutils will be required to use --gc-sections[1], which might require working around (Linux) package managers.
It'd just a recent version of DMD (after this is implemented) which is more likely to be manually installed (and frequently updated) anyway.


[1]: (Assuming R_arch_NONE isn't a recent feature)

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #4 from thomas-dloop@kuehne.cn  2007-04-25 12:56 -------
Walter, are you going to implement the R_arch_NONE solution or should we patch binutils?


-- 

http://d.puremagic.com/issues/show_bug.cgi?id=879


Brad Roberts <braddr@puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nfxjfg@gmail.com


--- Comment #5 from Brad Roberts <braddr@puremagic.com> 2010-08-29 12:35:37 PDT ---
*** Issue 4758 has been marked as a duplicate of this issue. ***

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Trass3r <mrmocool@gmx.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |mrmocool@gmx.de
           Platform|x86                         |All
            Version|1.00                        |D1 & D2
           Severity|enhancement                 |normal


--- Comment #6 from Trass3r <mrmocool@gmx.de> 2013-07-23 11:26:15 CEST ---
--gc-sections breaks everything, even hello world.

import std.stdio;
void main()
{
    writefln("FIXME!");
}

$ dmd -L--gc-sections -L--print-gc-sections test.d
ld: Removing unused section '.deh_eh' in file 'test.o'
ld: Removing unused section '.minfo' in file 'test.o'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__34_85a.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__54_915.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__5a_ff3.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__5e_8d3.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__60_fb1.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__62_882.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__63_f60.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(dmain2_44e_47b.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(dmain2_44e_47b.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_455_482.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_462_7db.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_467_46f.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_475_60d.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_478_6c8.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_47b_4cd.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_47c_53b.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_480_2a1.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(sections_linux.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__4db_e8d.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(console.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(container.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__551_86e.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(array.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(conv.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(exception.o)'
ld: Removing unused section '.minfo' in file
'libphobos2.a(exception_599_8af.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(format.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(functional.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(math.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(range.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(stdio.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(stdio_c2b_180.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(stdio_c2b_180.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(stdiobase.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(string.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(traits.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(typecons.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(typetuple.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(utf.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(object__6_32e.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(object__1b_3a8.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__57_ef0.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(runtime_e3_76e.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(runtime_e3_76e.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_12d_5a0.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(gc.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(gcx_2f3_8a.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(deh2.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__434_e4b.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(dmain2.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(lifetime.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_459_856.o)'
ld: Removing unused section '.deh_eh' in file
'libphobos2.a(lifetime_459_856.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_45e_4a3.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_461_4e2.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_463_4df.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_464_548.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_471_4c9.o)'
ld: Removing unused section '.deh_eh' in file
'libphobos2.a(lifetime_471_4c9.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(monitor_.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(tlsgc.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(algorithm.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(ascii.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(bitmanip.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(container.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(exception_5c8_d27.o)'
ld: Removing unused section '.deh_eh' in file
'libphobos2.a(exception_5c8_d27.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(random.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(regex.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(uni.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(uni_tab.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object_.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(exception.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__d9_929.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(runtime.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(runtime_e2_2e4.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(thread.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_109_236.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_10b_1b0.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_10e_330.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_10e_330.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_110_3bd.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_117_2e5.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_117_2e5.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_118_1b8.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_120_21c.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_124_28e.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_124_28e.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_126_48b.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_128_6e4.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_128_6e4.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_130_6f2.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_131_291.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_132_681.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_132_681.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_136_595.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_13a_85e.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_13e_762.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_13f_465.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_144_236.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_14e_1b8.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(time.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(time_177_5cc.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(mutex_225_213.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(gcx.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__343_b3c.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(critical_.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(dmain2_448_2f9.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(dmain2_448_2f9.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(dmain2_44a_2fd.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(dmain2_44a_2fd.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_46f_815.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_470_809.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(numeric.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object_891_87d.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(demangle_b8_ab6.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(demangle_b8_ab6.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_105_897.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_106_826.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_107_1b8.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_108_1b8.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_10a_22e.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_10a_22e.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_113_219.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_115_2d8.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_121_129.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_121_129.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_123_129.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_123_129.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_12e_726.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_12f_302.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_134_737.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_135_5f2.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_135_5f2.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_13b_469.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(time_16b_346.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(time_16b_346.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(time_178_297.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(time_17e_48a.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(time_17e_48a.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(aaA.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__340_aeb.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(lifetime_474_7cc.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(complex.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(demangle_b4_31d.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(demangle_b9_81f.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(demangle_b9_81f.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_104_713.o)'
ld: Removing unused section '.deh_eh' in file 'libphobos2.a(thread_104_713.o)'
ld: Removing unused section '.data' in file 'libphobos2.a(thread_119_155.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__341_c78.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__344_c36.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__345_be5.o)'
ld: Removing unused section '.minfo' in file 'libphobos2.a(object__33f_b6c.o)'

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--- Comment #7 from Trass3r <mrmocool@gmx.de> 2013-07-23 11:28:14 CEST ---
As far as I remember the flag works fine with gdc.

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